When i'm going like crusing speek from 0-65mph the car is fine, but when i go faster then that things shake or raddle, or vibrate, is this due to bad alignment, or screws lose, or something i havent thought of... just kinda curious.....

 

I have the same problem and I know a lot of other people have this issue in third gens. It really seams like a driveshaft issue when you think about it cause the driveshaft's speed is directly related to the speed of the car. So it seams that once you pass a certain speed it starts vibrating. So if that was the issue you would think getting it re-balanced would solve it. Problem is if you still see the balancing weights on it then why would it be out of balance. Well any way I have seen some people get results by getting the alluminum driveshafts. GM has them for about 200 bucks. I think I may just find a used stock one and get it balanced and swap it out and see what happens.

But this may not be the problem. There are other parts that move relative to the cars speed but those are the kind of things I would concentrate on.

 

or it could be you lost a weight on your tire, or the tires are underinflated, this is our problem with our minivan. (lol) if the rear tires are low on pressure, it vibrates like crazy at anything over 65. also the tires are cheap.........

 

Well my tires are about two years old, and i'm thinking the tread has gotten pretty low... so i may see what new tires do, and check out the drive shaft issue too. THanks a lot for your help!
TTT for more advise just in case.